DTS versus AC3

[Inventive Software]

I have a few DVDs. They all have AC3 audio, but 1 or 2 have a DTS stream with them as well. I know that DTS streams are generally encoded at a higher bitrate than AC3 streams (768-1536 Kbits/sec for DTS vs 192-448 Kbits/sec for AC3).

My question is what has the higher quality, DTS or AC3, and is it distinguishable to the human ear?

Just because DTS has the higher bitrate doesn't mean it's a better quality, right?

[Mr. Monte]

I have a few DVDs. They all have AC3 audio, but 1 or 2 have a DTS stream with them as well. I know that DTS streams are generally encoded at a higher bitrate than AC3 streams (768-1536 Kbits/sec for DTS vs 192-448 Kbits/sec for AC3).

My question is what has the higher quality, DTS or AC3, and is it distinguishable to the human ear?

Just because DTS has the higher bitrate doesn't mean it's a better quality, right?

Since this seems borderline "which is best" no-no...I'll answer my two cents.

From all my listening (Denon AVR3803 with 6.1 surround..I believe DTS sounds better.

Now alot will tell you that is becasue DTS tracks are typically recorded at a higher volume than AC3 also. Higher bitrate "should" mean better, as long as its compare from the same source. However mixing might play a role also.

[ursamtl]

The pro-AC3 folks on here usually make the argument that when studios release DVDs with both AC3 and DTS tracks they use a different mix. This may be true in some cases, especially for movies where there were mixes initially done for theatrical releases, but certainly for music DVDs the trend is towards one mix for the stereo track and another for the 5.1 track. If the 5.1 includes both AC3 and DTS, then the same mix will be used for both.

It's been my experience in A-Bing such discs that the DTS tracks sometimes tend to sound slightly better, but there are so many variables that it's almost impossible to make a definitive statement. I have heard discs where the AC3 track sounded a bit better. Then one has to be careful about the psychological effect of expectations, i.e., if one expects a track to sound better, it will! the DTS tracks that sounded better to me weren't louder per se; they usually exhibited better frequency response, with crisper highs and deeper bass. Overall, they tended to sound a bit more open or airy, less boxy, more natural and with greater dynamic range.

The pro Dolby people will always produce studies, facts and figures to back their side. The DTS afficionados will do the same. Both web sites are full of convincing materials to back their superiority over the rival system. It kind of reminds me of the DVD-A versus SACD debate.

The perception is definitely out there that DTS=better quality. This becomes a marketing tool, which in turn feeds the perception further. This would seem to give DTS the edge. Plus, as you mentioned, the higher bitrate would suggest better quality. Of course, this argument would only be valid if the encoding process were the same, which it's not (as Dolby fanatics are very quick to point out :) ). Dolby definitely has an advantage in that a 5.1 AC3 track downmixes to playback on 2-channel systems whereas a DTS track will only play through a DTS decoder. Plus Dolby has been in the surround business so long that people tend to associate it with quality sound. All those Dolby NR buttons on cassette decks over the years certainly helped with that association as well.

So, in the end, it's probably 75%-85% perception with the rest based on whichever scientific study a person tends to believe more. Personally, if a disk has a DTS track, I almost always switch to it. Occasionally I'll A-B, but most of the time, I just sit back and enjoy the surround sound immensely!

[Audionut]

The were numorus reports in selected media in australia reguarding problems with the DTS mixing when it first appeared here.

ie: sounds were not being placed correctly in the mix.

IMHO, the Dolby track always sounds more natural to me.
The DTS track has more punch/kick/energy. But it lacks something, that makes me select it.

[Inventive Software]

So again it comes down to personal preference.

AC3 generally sounds crap on my computer without DRC, but it may be to do with my crap speakers (they're about 10 years old!!). I can't hear any difference between the two, apart from DTS doesn't really need any sort of DRC or normalizing.

Personally I think I'll stick with AC3, just because so much more supports it when transcoding. Usually I'll use the AC3 stream because it's easier to manipulate in say AviSynth. But that is just personal preference.

[kurt]

like urmsamtl said, i prefer dts.
it sounds often (Underworld, Master&Commander..) more powerful and that is what i like :D
@ Audionut: it has less naturalness? I am unaware of that yet...

[ursamtl]

like urmsamtl said, i prefer dts.
it sounds often (Underworld, Master&Commander..) more powerful and that is what i like :D
@ Audionut: it has less naturalness? I am unaware of that yet...

Yes, the soundtrack to Master & Commander sounds much better in DTS than AC3. That was one case where A-Bing revealed a much more powerful DTS track. It didn't seem like a different mix, just a much more dynamic and natural sounding version of the same thing. It reminded me of comparing a cheap Radio Shack stereo (AC3) with a decent audio store listening room system. But, as I said, I've also heard AC3 tracks that sounded better.

[Teegedeck]

We only know whether the actual DTS soundtracks on DVDs sound better than their AC3 equivalents. This has got very little to do with the codec's quality: Because if the DTS mix sounded worse than the AC3 mix, having DTS on that DVD simply wouldn't be of any marketing value, would it?

DTS seems to be advertised as 'better because of higher bitrate' and so actually existing DTS soundtracks probably are, if only for the higher bitrate. (Or for being encoded at a higher volume; more 'bang' because the public loves that - like pop music is experiencing a 'loudness war', too.) If you think of it, otherwise encoding DTS at higher bitrates than AC3 could only mean that DTS is worse than AC3 and thus needs more bits to reach the same quality - and I don't believe that is true. So it is kind of a superiority by marketing design. ;)

The only way to tell whether DTS is a better codec than AC3 would be to encode PCM audio with high-quality DTS and AC3 encoders and compare in a blindtest. Obviously, we won't see such a test.

From a probability-based point of view, DTS, having roots as old as AC3, should be a much worse codec than Vorbis, MPC or AAC which all are based on more modern designs. Of which only AAC has good surround capabilities, of course.

But that is pure theory and not really relevant, because all you have on a DVD are AC3 and DTS soundtracks to choose from, both are encoded with rather old and dated codecs.

To end this strange competition of 'which audio codec uses higher bitrates' I am really keen to see whether BluRay will bring us uncompressed sound (or lossless) and that way put an end to the debate. :)

[Mr. Monte]

To end this strange competition of 'which audio codec uses higher bitrates' I am really keen to see whether BluRay will bring us uncompressed sound (or lossless) and that way put an end to the debate. :)

Why wouldn't blueray use an AAC/MPC?

[KpeX]

Why wouldn't blueray use an AAC/MPC?With 50 gigs of space to play with and lossless codecs being rather efficient these days, it would make more sense to use lossless audio. The size difference between quality lossy audio and lossless audio on a 50 gig disc is not worth the loss.

[Backflip]

Just out of interest, how large would lossless multichannel audio be in a typical movie? (What's the math to work that out?)

[johnman]

The typical compression of lossless codecs reduces the size with 40%.

[Mr. Monte]

The typical compression of lossless codecs reduces the size with 40%.

Lossless..like Monkey's Audio or FLAC?

[zambelli]

Just out of interest, how large would lossless multichannel audio be in a typical movie? (What's the math to work that out?)

Give it a try. WMA Professional supports lossless compression up to 6 channels (at 96kHz 24bit).

[ursamtl]

Give it a try. WMA Professional supports lossless compression up to 6 channels (at 96kHz 24bit).

Unfortunately, there aren't many settop devices that support it, meaning that most DVD players won't play it.

[Chainmax]

Sorry for the slight hijack, but what really is the point of multichannel encoding? If one has a 192kbps stereo and 448 kbps 5.1 version of a soundtrack, wouldn't the stereo one sound better than the 5.1 one (regardless of codec used)?

[Mug Funky]

the DVDs that come out of here have the same mix for DTS and AC3 (we rarely use DTS though).

as far as quality, well, i've never done an ABX test with the original DA-88 tape as reference, as this would be exceedingly hard an experiment to set up (the machine room is loud as hell, not really amenable to ABX testing).

one reason for the different tone and dynamics might be the mixdowns that happen on 2.0 systems - i find the AC3 is always louder and the LFE always too loud (even with DRC turned off).

technically, ac3 is more efficient by a long way, and half-rate DTS tends to lose a lot of high end. i've not noticed this from normal movie watching though. full-rate DTS should sound the best, but of course you sacrifice video quality and extras to fit these on the disc...

[ursamtl]

Depends what the listener wants. When A-Bing between 2.0 and 5.1 versions of the same audio program, it's really difficult to stick with the 2.0 version (unless there is a really noticeable degradation of sound). It's very similar to going from stereo back to mono. the soundfield collapses too much.

[Chainmax]

the soundfield collapses too much.

Sorry if my ignorance shows too much, but what do you mean by that?

[ursamtl]

I mean that a 5.1 audio track when played back through a 5.1 system sounds amazing compared to stereo. When one switches back to stereo, the whole rear soundfield disappears. It's like closing a door and listening through the keyhole!